Research and analysis on the in-situ repair technology of subway tunnels using a combination of liquid nitrogen and saltwater freezing
Based on an in-depth analysis of emergency handling techniques for the phenomenon of water gushing and sand eruption in the field of urban infrastructure underground engineering in China,and in response to the problems existing in the water sealing and reinforcement technologies used in soft and water-rich strata at home and abroad,a composite freezing construction method combining liquid nitrogen and brine has been proposed to cope with emergencies.Firstly,in the case of shallow-buried large-section tunnel excavation in complex building environments where groundwater flow may cause erosion to the soil,a tunnel reinforcement filling technology has been proposed.Subsequently,consid-ering the problem that conventional cement slurry and water-containing materials are prone to freezing and blocking under low-temperature conditions,a technology using brine cement slurry for filling and freezing pipe construction has been proposed.Finally,the effectiveness of the proposed technology was evaluated through data collected by on-site monitoring.The research results show:① During the freezing process,the temperature of the stratum and the surface settlement deformation were effec-tively controlled,successfully forming a solidified body and a water stop barrier,which not only shortened the freezing cycle of liquid nitrogen and brine but also improved the quality of the freezing wall;(2)The liquid nitrogen freezing technology played a role in sealing and reinforcing the excavated area,ensuring the sealing of the foundation pit and tunnel during drainage and dredging,effectively resisting water and soil pressure,and cutting off the connection between the intact tunnel and the sur-rounding soil,enhancing the stability of the tunnel;③ By combining the rapid freezing characteristics of liquid nitrogen and the reinforcement effect of brine,the technology not only significantly shortened the repair time but also greatly improved the safety of the construction process.The successful appli-cation of this technology provides effective technical support for the repair of subway tunnels under complex geological conditions and has important engineering value and social benefits.
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